What is influenza virus vaccine?

Influenza virus (commonly known as "the flu") is a serious disease caused by a virus. Influenza virus can spread from one person to another through small droplets of saliva that are expelled into the air when an infected person coughs or sneezes. The virus can also be passed through contact with objects the infected person has touched, such as a door handle or other surfaces.

Influenza virus vaccine is used to prevent infection caused by influenza virus. The vaccine is redeveloped each year to contain specific strains of inactivated (killed) flu virus that are recommended by public health officials for that year.

The injectable influenza virus vaccine (flu shot) is a "killed virus" vaccine. Influenza virus vaccine is also available in a nasal spray form, which is a "live virus" vaccine.

Influenza virus vaccine works by exposing you to a small dose of the virus, which helps your body to develop immunity to the disease. Influenza virus vaccine will not treat an active infection that has already developed in the body.

Influenza virus vaccine is for use in adults and children who are at least 6 months old.

Becoming infected with influenza is much more dangerous to your health than receiving this vaccine. Influenza causes thousands of deaths each year, and hundreds of thousands of hospitalizations. However, like any medicine, this vaccine can cause side effects but the risk of serious side effects is extremely low.

Like any vaccine, influenza virus vaccine may not provide protection from disease in every person. This vaccine will not prevent illness caused by avian flu ("bird flu").

What is the most important information I should know about this vaccine?

The injectable influenza virus vaccine (flu shot) is a "killed virus" vaccine. Influenza virus vaccine is also available in a nasal spray form, which is a "live virus" vaccine. This medication guide addresses only the injectable form of this vaccine.

Becoming infected with influenza is much more dangerous to your health than receiving this vaccine. However, like any medicine, this vaccine can cause side effects but the risk of serious side effects is extremely low.

What should I discuss with my healthcare provider before receiving this vaccine?

You may not be able to receive this vaccine if you are allergic to eggs, or if you have:

a history of severe allergic reaction to a flu vaccine; or

a history of Guillain-Barre syndrome (within 6 weeks after receiving a flu vaccine).

To make sure influenza virus injectable vaccine is safe for you, tell your doctor if you have:

a bleeding or blood clotting disorder such as hemophilia or easy bruising;

a neurologic disorder or disease affecting the brain (or if this was a reaction to a previous vaccine);

a history of seizures;

a weak immune system caused by disease, bone marrow transplant, or by using certain medicines or receiving cancer treatments; or

if you are allergic to latex rubber.

You can still receive a vaccine if you have a minor cold. In the case of a more severe illness with a fever or any type of infection, wait until you get better before receiving this vaccine.

Vaccines may be harmful to an unborn baby and generally should not be given to a pregnant woman. However, not vaccinating the mother could be more harmful to the baby if the mother becomes infected with a disease that this vaccine could prevent. Your doctor will decide whether you should receive this vaccine, especially if you have a high risk of infection with influenza.

It is not known whether influenza virus vaccine passes into breast milk or if it could harm a nursing baby. Do not receive this vaccine without telling your doctor if you are breast-feeding a baby.

This vaccine should not be given to a child younger than 6 months old.

How is this vaccine given?

Some brands of this vaccine are made for use in adults and not in children. Your child's doctor can recommend the best influenza virus vaccine for your child.

This vaccine is given as an injection (shot) into a muscle. You will receive this injection in a doctor's office or other clinic setting.

You should receive a flu vaccine every year. Your immunity will gradually decrease over the 12 months after you receive the influenza virus vaccine. Children receiving this vaccine may need a booster shot one month after receiving the first vaccine.

The influenza virus vaccine is usually given in October or November. Some people may need to have their vaccines earlier or later. Follow your doctor's instructions.

Your doctor may recommend treating fever and pain with an aspirin-free pain reliever such as acetaminophen (Tylenol) or ibuprofen (Motrin, Advil, and others) when the shot is given and for the next 24 hours. Follow the label directions or your doctor's instructions about how much of this medicine to give your child.

It is especially important to prevent fever from occurring in a child who has a seizure disorder such as epilepsy.

What happens if I miss a dose?

Since flu shots are usually given only one time per year, you will most likely not be on a dosing schedule. Call your doctor if you forget to receive your yearly flu shot in October or November.

If your child misses a booster dose of this vaccine, call your doctor for instructions.

What happens if I overdose?

An overdose of this vaccine is unlikely to occur.

What should I avoid before or after receiving this vaccine?

Follow your doctor's instructions about any restrictions on food, beverages, or activity.

Influenza virus injectable vaccine side effects

Influenza virus injectable (killed virus) vaccine will not cause you to become ill with the flu virus that it contains. However, you may have flu-like symptoms at any time during flu season that may be caused by other strains of influenza virus.

You should not receive a booster vaccine if you had a life-threatening allergic reaction after the first shot.

Keep track of any and all side effects you have after receiving this vaccine. If you ever need to receive influenza virus vaccine in the future, you will need to tell your doctor if the previous shot caused any side effects.

Get emergency medical help if you have signs of an allergic reaction: hives; difficulty breathing; swelling of your face, lips, tongue, or throat.

Call your doctor at once if you have:

a light-headed feeling, like you might pass out;

severe weakness or unusual feeling in your arms and legs (may occur 2 to 4 weeks after you receive the vaccine);

high fever;

seizure (convulsions); or

unusual bleeding.

Common side effects may include:

low fever, chills;

mild fussiness or crying;

redness, bruising, pain, swelling, or a lump where the vaccine was injected;

headache, tired feeling; or

joint or muscle pain.

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report vaccine side effects to the US Department of Health and Human Services at 1-800-822-7967.

If you are using any of these medications, you may not be able to receive the vaccine, or may need to wait until the other treatments are finished.

This list is not complete. Other drugs may affect influenza virus injectable vaccine, including prescription and over-the-counter medicines, vitamins, and herbal products. Not all possible interactions are listed in this medication guide.

Further information

Remember, keep this and all other medicines out of the reach of children, never share your medicines with others, and use this medication only for the indication prescribed.